The goal for this R03 application is to identify causal gene variants linking colon cancer and tooth agenesis. Colon cancer is common and is the second most lethal cancer in the world, with approximately 600,000 related deaths/year worldwide. Tooth agenesis is defined as the failure to develop one or more permanent teeth, and is the most common congenital anomaly in humans. A single report showed the segregation of colon cancer and tooth agenesis in a four-generation Finnish family and suggested a common etiology between the two conditions. However, to date, there have been no systematic clinical or molecular studies of tooth agenesis in colon cancer families to confirm the findings of that initial report and to discover genetic variants contributing to a combined phenotype on a genome-wide scale. For this proposal, we have searched the records of the NIH Colon Cancer Family Registry and selected twenty probands presenting with colon cancer and tooth agenesis, and family history of tooth agenesis, for use in next generation sequencing experiments to identify causal gene variants linking colon cancer and tooth agenesis. Clinical data and DNA samples are readily available in the PI's laboratory. We propose two aims to accomplish this project: (1) DNA samples of the twenty unrelated probands will be subjected to whole exome sequencing (WES) of all known human genes followed by massively parallel sequencing of the captured targets. WES is a powerful approach that has revolutionized our ability to identify disease-causing mutations. Novelty of variants will be assessed by filtering th variants using information that are available in public databases and unlikely disease causing variants will be filtered out. Bioinformatics will be used for candidate gene prioritization, based on predicted functional impact and gene expression data; (2) Prioritized variants will be confirmed in probands and genotyped in selected relatives with tooth agenesis only using Sanger sequencing and/or Sequenom genotyping. The results of this study will allow the identification of gene(s) that are enriched with damaging mutations and thus likely to be contributing to the combined phenotype. Further, the results will delineate a broader phenotype spectrum to which tooth agenesis and colon cancer may belong, and determine if tooth agenesis may be considered an early clinical marker for colon cancer predisposition in susceptible families. The identified variants may be used as screening tools for increased colon cancer susceptibility in additional tooth agenesis families, allowing for improved identification o at-risk families, referral to genetic counseling, and ultimately cancer prevention. The study team presents the expertise and motivation necessary to lead the proposed research. This work will be the basis to a future R01 application to validate or find other variants in additional colon cancer families and tooth agenesis families, and to investigate the molecular mechanisms of the variants identified using in vitro and in vivo models. Finally, the results of this study may revea a paradigm-shifting approach with wide applicability in the dental profession, as dentists will play critical role in identifying families with tooth agenesis at risk for colon cancer.